Mighty Max ML18-12 12V 18 Ah AGM Battery

Mighty Max ML18-12 battery is Sealed Lead Acid (SLA) Absorbent Glass Mat (AGM) featuring 18 Ah capacity and 12 volts nominal voltage.

Mighty Max ML18-12 battery is very popular general purpose battery, often used in both cyclic and standby applications like portable tools, generators, lawn and garden tools, electric vehicles, power sports, toys, various hobbies etc.

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Mighty Max ML18-12 Battery Features and Specifications

Mighty Max ML18-12 battery is AGM battery, featuring electrolyte (diluted sulfuric acid) absorbed and immobilized by glass mat. Also, it is SLA battery, featuring safety valve that release excess hydrogen and oxygen, but not the electrolyte - it is spill-proof battery, being able to operate in virtually any position.

Mighty Max ML18-12 battery is 'almost' maintenance free battery - we say 'almost' since many people literally think that AGM SLA batteries are fully maintenance free batteries. The only maintenance required is keeping terminals clean and charging/maintaining the battery when it is discharged or not in used for longer period of time.

Mighty Max ML18-12 battery physical dimensions are (L x W x H) 7.13 x 3.03 x 6.57 inches (181 x 77 x 167 mm) and it weighs ~11.2 pounds (5.1 kg).

Its nominal voltage is 12 volts and nominal (20h) capacity is 18 Ah and its fully charged battery internal resistance is 16 mΩ.

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Mighty Max ML18-12 battery features 'nuts and bolts' types of terminals, as one can see in the photo - negative terminal is on the left and positive terminal (red base) is on the right side of the battery, when the battery is watched from its front side.

Mighty Max ML18-12 battery capacity depends on the discharge current and it is given in the following chart:

Discharge Time End Voltage Current Capacity (77°F, 25°C)
20 hours 10.5V (1.75V/Cell) 0.9 Amps 18 Ah
10 hours 10.5V (1.75V/Cell) 1.62 Amps 16.2 Ah
5 hours 10.5V (1.75V/Cell) 2.9 Amps 14.5 Ah
1 hour 9.6V (1.6V/Cell) 11 Ams 11 Ah
1 hour 10.5V (1.75V/Cell) 10 Amps 10 Ah

Note: it is not recommended to discharge AGM SLA batteries below 10.5 volts, as that can shorten their operating life (number of charging/discharging cycles, effective capacity, etc.).

Like all other lead-acid batteries, Mighty Max ML18-12 battery capacity is decreased as the discharge current is increased.

Battery capacity is also affected by the temperature of the battery:

- at 104°F (40°C), Mighty Max ML18-12 battery features 102% of its nominal (77°F, 26°C) capacity,

- at 32°F (10°C), Mighty Max ML18-12 battery features 85% of its nominal (77°F, 26°C) capacity,

- at 5°F (-15°C), Mighty Max ML18-12 battery features 65% of its nominal (77°F, 26°C) capacity.

Such capacity loss is common in lead-acid batteries and must be carefully calculated when such batteries are used during the winter.

Mighty Max ML18-12 battery features rather low self-discharge rate and when being stored at 68°F (20°C) its capacity loss is:

- 3 months storage: at 90% SoC,

- 6 months storage: at 80% SoC,

- 12 months storage: at 60% SoC.

Personally, when the battery reached 80% SoC (State of Charge), charge it back again. Or even better, connect it to the intelligent, microprocessor controlled charger/maintainer that will constantly monitor battery condition and act as required.

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Maximum allowed discharge current is 255 Amps for 5 seconds at 77°F (25°C).

Discharge features of the Mighty Max ML18-12 battery are given in the following constant current discharge chart (Amps at 77°F, 25°C) and constant power discharge chart (watts at 77°F, 25°C):

Mighty Max ML18-12 Battery Constant Current Discharge (Amps at 77°F, 25°C)

End Voltage per Cell 5 min 10 min 15 min 30 min 1 hour 3 hours 5 hours 10 hours 20 hours
1.60 volts 63.7 42.8 32.6 19.2 11.0 4.49 3.05 1.68 0.89
1.65 volts 61.4  41.8  31.8  18.8  10.7  4.40  3.00  1.66  0.88
1.70 volts 59.1  40.8  31.0 18.4  10.4  4.30  2.95  1.64  0.87
1.75 volts 56.8  39.6  30.2  18.0  10.0  4.21  2.90  1.62  0.85
1.80 volts 54.5  38.6  29.4 17.5  9.7  4.12  2.85  1.60  0.84

Mighty Max ML18-12 Battery Constant Power Discharge (watts at 77°F, 25°C)

End Voltage per Cell 5 min 10 min 15 min 30 min 45 min 1 hour 2 hours 3 hours 5 hours
1.60 volts 774 490 389 228 167 134 87 63 41.3
1.65 volts 750 475 380 221  161  129  81.6  59 39.4
1.70 volts 720 456 365 214  154  122  76.8  54.5 37.4
1.75 volts 678 436 350 206  147  116  72  49.7 35.3
1.80 volts 642 415 336 197  139  108  65.4  44.3  32.8

Few notes: if possible, don't discharge your AGM SLA batteries below 1.75 volts per cell (10.5 volts per battery). Also, Mighty Max ML18-12 battery is designated as 18 Ah battery, but when constant discharge current for 20 hours down to 10.5 volts (1.75 volts per cell) is checked, discharge current is 0.85 Amps, giving actual capacity of 17 Ah and NOT 18 Ah.

Such data deviations are possible (and happen all the time and to every manufacturer), not  and within acceptable limits - after all, not many manufacturers state provide such detailed information about their batteries.

Mighty Max ML18-12 battery comes with 1-year warranty which is very important when being used in both cyclic and standby use.

When being used for cyclic applications, it is important to know that battery's current capacity depends on the number of charge/discharge cycles and Depth of Discharge (DoD - 'opposite' of State of Charge SoC), which is given in the following chart:

Capacity (% of nominal capacity) 100% DoD 50% DoD 30% DoD
80% (~14.4 Ah) ~175 ~350 ~850
60% (~10.8 Ah) ~200 ~420 ~1150

So, after ~175 cycles down to 100% DoD, battery will have ~80% of its nominal capacity (~14.4 Ah). Similarly, after ~1150 cycles down to 30% DoD (or 70% of SoC), battery will still retain ~60% of its nominal capacity (~10.8 Ah).

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How to Charge Mighty Max ML18-12 Battery

battery charger small mDepending on its use, Mighty Max ML18-12 battery should be charged at 13.6 - 13.8 volts (float use, 77°F, 25°C) or 14.5 - 14.9 volts (cyclic use, 77°F, 25°C, 5.4 Amps maximum charging current).

Mighty Max ML18-12 battery can be charged using simple SLA AGM charger, although smart, intelligent AGM SLA battery charger/maintainer is recommended.

Since this battery is commonly used on fishing, camping, hunting and similar trips, people regularly charge them with solar panels with peak power of 5-6 Amps. Such solar panels, even when conditions are not ideal, they are able to provide at least 20-25 Ah of charge during a daylight, which is enough to fully charge fully discharged Mighty Max ML18-12 battery.

If stronger solar panels are required, be sure to limit the charging current to ~5 Amps and charging cutoff voltage to 14.5-14.9 volts.

For more about AGM battery chargers, check our Tools and Accessories pages.

Mighty Max ML18-12 Battery as Fish Finder Battery

Mighty Max ML18-12 battery is commonly used as fish finder battery, especially on smaller boats, pontoon, kayaks and rafts.

Mighty Max ML18-12 battery is simple to charge and maintain, and it is relatively lightweight (11.2 pounds, 5.1 kg).

garmin striker mFish finders come in various sizes and shapes, differing in transducer power, computer power, display size, some of them even feature WiFi, Bluetooth, or LAN connectivity, etc.

Like fish finders, their consumption varies, from ~0.2 Amps for smaller, compact models, to 2-3 Amps (or even more) for large, powerful fish finder/GPS/chartplotter combo units.

Small, compact fish finders requiring just ~0.5 Amps can be powered with Mighty Max ML18-12 battery for at least ~36 hours (1 day and 12 hours), assuming brand new, fully charged battery at 77°F (25°C).

Larger units requiring for example 2.90 Amps, can be powered using this battery for ~5 hours - and that is a lot of power for a fish finder.

For example, one of the most popular, compact and rather versatile fish finders Garmin Striker 4 GPS Fish Finder (Amazon link, opens in the new window), draws ~0.23 Amps, when being powered with 12V source.

Mighty Max ML18-12 battery is an excellent choice for fish finder battery - it is cheap, reliable and it isn't too heavy, especially not when being compared with large dual purpose SLA AGM batteries commonly found in the boat's single-battery electrical systems.

Mighty Max ML18-12 Battery as Trolling Motor Battery

Mighty Max ML18-12 battery can be even used as trolling motor battery, but only for smaller/weaker trolling motors, like electric trolling motors found on kayaks and small rafts/pontoons.

When being discharged down to 10.5 volts, Mighty Max ML18-12 can provide 30 Amps for 15 minutes, 18 Amps for 30 minutes, 10 Amps for 1 hour etc. If you have the need for stronger electric trolling motor or for longer operating time, you will need larger battery.

Mighty Max ML18-12 Battery as Starting Battery

Mighty Max ML18-12 battery is not intended for starting large petrol and diesel engines.

But, with 255 Amps for 5 seconds, it is commonly used as dual-purpose battery in electric generators, ride-on lawn mowers, power sports, ATVs, snowmobiles etc.


mighty max ml18 12 agm mLong Story Short: If you are looking for the battery in this size and capacity range, and this battery fits your need, consider it: it has good charging and discharging characteristics, low self-discharge rate, comes at acceptable price etc.

After all, it is very popular model, used (and sometimes abused) by countless users who tested it in many real life situations.

For more reviews and recommendations, check Mighty Max ML18-12 Battery Amazon link (link opens in the new window).